1. Field of the Invention
The present invention relates generally to a laser surveying system and, more particularly, to a laser surveying system for measuring a displacement such as a sinkage of a structure, a ground subsidence and a distortion change of a bridge.
2. Related Background Art
FIG. 11 illustrates a conventional laser surveying system for measuring a displacement such as a sinkage of a structure, a ground subsidence and a distortion change of a bridge. Referring to FIG. 11, a light projector 1 is installed at an unmovable point. Mounted next at measuring points of a structure 2 are a plurality of laser beam position detecting devices 3, 4, 5, 6 for obtaining pieces of positional data of laser beams. For transmitting the obtained positional data of the laser beams, positional data output codes 7 are distributed from the laser beam position detecting devices 3, 4, 5, 6 and then connected to a multiplexer 8. With respect to a quantity of sinkage of the structure, the positional data outputted from the laser beam position detecting devices 3, 4, 5, 6 can be sequentially selected by the multiplexer 8, and, therefore, the outputs from the multiplexer 8 are data-processed by a personal computer 9, thus making it possible to analyze a state of the sinkage of the structure 2.
The light projector 1 constituting this laser surveying system includes a light projection mechanism unit structured as illustrated in FIG. 12. Laser beams from a laser diode 11 are collimated by a collimating lens 12 into substantially parallel laser beams and thereafter deflected by a reflecting mirror 13. The thus deflected laser beams L are emitted in a horizontal direction. The laser beams L are always emitted in the horizontal direction by an auto compensator constructed of a movable cylinder 14 and a fixed cylinder 15. The reflecting mirror 13 is fixed to a rotary unit 16 but rotatable, thus forming a horizontal laser surface. An emerging direction of the laser beams L can be set in directions exclusive of the horizontal direction by using a prism for changing an angle thereof.
Further, FIG. 13 is a front view of a light receiving device but includes a circuit diagram. As illustrated in FIG. 13, in the laser beam position detecting devices 3, 4, 5, 6 constituting this laser surveying system, a light receiving device 18 is constructed of a light receiving element 18a having a wedge-like shape expanding upward from under and a light receiving element 18b having a wedge-like shape expanding downward from above. Rates of light receiving quantities of the light receiving elements 18a, 18b change depending on a height position of an incidence of the laser beams L. Output signals S1A, S1B from the light receiving elements 18a, 18b are processed by a detection circuit 19 and an output circuit 20, thereby outputting a height position signal.
Further, Japanese Patent Publication No. 4-56243 discloses a level for a specific height measurement which includes an image sensor constructed of a string of reading elements and capable of digital direct reading and displaying on the basis of an image output of the image sensor by use of symbolic patterns formed on a levelling rod, corresponding to height values.
In the above-mentioned laser surveying system, however, the laser beam position detector outputs the positional data of the laser beam as electrical positional data. Hence, codes for outputting the positional data have to be distributed in order to connect the laser beam position detector to a multiplexer. Consequently, there arises a problem in which a mounting position of the laser beam position detector is confined to a code distributable position in terms of a necessity for distributing the codes. There also exists a problem in which, when the number of measuring points increases, the code distribution becomes correspondingly complicated, resulting in a difficulty of distributing the codes.
There is also such a problem that the laser beam position detector is expensive, and the price rises with a greater number of measuring points. A further problem is that the laser beam position detector is large in weight, enough to deform a measured object such as a structure or the like, and this exerts an adverse influence on the measured value.
Moreover, the above-mentioned conventional laser surveying system is capable of making a one-dimensional measurement of the displacement but is incapable of making two- and three-dimensional measurements of the displacement. There further arises a problem in which such measurements of the displacement have to be done by other expensive measuring devices.
The technique disclosed in Japanese Patent Publication No. 4-56243 involves the use of the intricate symbolic patterns and entails focusing of the level on the levelling rod. For this reason, it is required that the levelling rod be illuminated with light, and, if focused on a plurality of levelling rods, it is difficult to quickly effect focusing on each levelling rod.